1. Field of the Invention
The instant disclosure relates to a push-fit ring-seal joint structure for plastic pipes; more particularly, to an improved joint structure that has an inwardly tapered lip portion and an immediately followed throat portion having two continuously adjacent stepped V-shaped ridges, where the outer ridge toward the lip portion defines an O-ring receiving region, while the inner ridge defines a deflection tolerating zone, thus allowing the instant joint structure to accommodate angular deflection up to three or four times greater than the conventional push-fit joint, while providing excellent sealing and pressure rating.
By using the joint structure of the instant disclosure, particularly through its unique structural design, greater pipe deflection can be tolerated. Therefore, when encountering ground movement (e.g. ground subsidence, earthquake) or adjustment of pipe route during installation, the joint structure of the instant disclosure can still maintain excellent sealing and pressure rating.
2. Description of Related Art
The applicant of the instant disclosure is the largest PVC pipe manufacturer in Taiwan with excellence in quality. Various types of plastic pipes developed by the applicant have been used widely in the domestic market. The popularity derives from the unique design of the pipes itself, along with other attributes such as high pressure rating, excellent sealing, and ease in installation. Particularly in the advancement and upgrade of connecting techniques of the PVC pipes, the applicant has made many contributions and provided numerous technological breakthroughs.
However, particularly after the deadly 921 earthquake (also known as the September twenty first Jiji Earthquake) in Taiwan, the plastic pipes that were put in service are in need for upgrade. Besides better impact resistance, the plastic pipe, particularly its pipe joints, needs to be able to maintain effective sealing and withstand high water pressure during ground movements due to earthquakes or adjustment of route during installation.
Please refer to FIG. 1, which shows a longitudinal cross sectional view of a conventional push-fit joint 20 for a plastic pipe. The inner circumferences of a lip portion 30 and a throat portion 40 thereof are smooth and substantially cylindrical. When another pipe having a plain spigot (the male pipe) is received by the conventional push-fit joint 20, very small clearances exist between the two pipes, such that the spigot end is snugly received therein as in a socket. For curved pipe route, the joining of the male and female ends of the pipes becomes more difficult. If the coupling is done forcibly, a rubber seal 50 can easily be jammed and cause leakage. Another limitation is even if the pipes are successfully jointed, the allowable angular deflection, represented by α in FIG. 2, is approximately 3°˜4°. In addition, as shown in FIG. 2, the portion where the lip portion 30 merges into the throat portion 40 is prone to be damaged. Further still, if the pressure distribution over the rubber seal 50 is not uniform, the pipe joint is subject to leakage. If the construction site is poorly maintained, leakage problems due to poor field handling are even more likely to occur.
To provide ease of laying the pipe work, the conventional push-fit joint 20 is normally designed such that some clearances exist between the inner circumference of the lip portion 30 and the spigot of the inserted pipe. The rubber seal 50 is elastic and has a hardness value ranging from 50˜65 shore A. The shore A scale is used as a measure of hardness in rubbers and ranges from 0 to 100, with 0 being extra soft and 100 being extra hard. However, in practice, after the pipe installation is completed, the rubber seal 50 is often forced out of position by the pressurized fluid. As a result, the conventional push-fit joint tends to loose its sealing ability and is subject to leakage. When the pipe route must be adjusted to fit the terrain, the manner in which the inserted pipe is deflected often creates clearances inside the conventional push-fit joint disproportionally, which increases the likelihood of leakage. As previously mentioned, a large leak can result from the rubber seal 50 being pushed out of position by excessive pressure of the running fluid. To avoid the abovementioned problems, if a smaller clearance is proposed between the two pipes at the lip portion 30, the pipes would become much harder to couple, taking more time and effort. In particular, when the pipe route needs to be adjusted because of the terrain, the proposed clearance reduction would only exacerbate the coupling difficulty. If the joining of pipes is done forcibly, the rubber seal 50 would be pushed out of position, as the conventional push-fit joint 20 looses its sealing ability and allows leakage to occur. Likewise, if a harder rubber seal 50 is used to prevent the displacement from happening, the coupling of the pipes would be more difficult and the sealing of the pipes would not be as effective.
Moreover, Taiwan (where the Applicants reside) is located in an area where seismic activity happens frequently. Ground movement associated with an earthquake often causes damages at pipe joints where leakage would occur.